If an SCP-XXXX-1 instance is located prior to stage 1 infection, the individual instance must be captured prior to entering stage 1 infection.

If possible, SCP-XXXX-1 instances must be detained before stage-1 infection occurs.

Instances are to be kept in a Level Blue humanoid containment chambers and monitored at all times for the purposes of research and the possibly creation of a cure for SCP-XXXX.

Chamber*, possible*.

If an SCP-XXXX-1 instance currently contained by the Foundation enters into stage 1 of the infection, Foundation personnel are to terminate that individual instance of SCP-XXXX-1 and to destroy all SCP-XXXX-2 instances.

Try to phrase this better, like above. You have one sentence that takes up three lines.

Currently, the development of a cure for SCP-XXXX is considered the best plan of action for the Foundation in terms of containing SCP-XXXX.

Highest priority?

The pathogen primarily infects biological humans

As opposed to mechanical ones?

The interview logs and the letters are…an interesting addition. I think it definitely helps the article to include the point of view that the victims go through. Maybe not like this though. I didn't feel it.